In the prior art, mirrors used, for example, in large ground based and spaced based telescopes, include a honeycomb core disposed between the mirror surface and a backing plate. See U.S. Pat. Nos. 4,331,383; 6,045,231; 5,076,700; 4,447,130; 3,754,812; 4,917,934; 3,507,737; 3,644,022; 4,466,700; and 4,692,367 incorporated herein by this reference.
The honeycomb core supports the mirror and is light weight—an important feature for the back structure of the mirror since the mirror and the rest of the components of the telescope are repositioned by various motors. Especially in space-based applications, it is critical that all of the components of the telescope be as lightweight as possible since the maneuvering motors associated with the telescope and spacecraft have limited power available and because the telescope itself must be transported via the space shuttle or a rocket.
But, as the glass reflecting surface is made thinner and thinner to reduce its mass, the local bending stiffness is reduced at a rate of proportional to the cube of the thickness. As the glass bending stiffness is reduced, the honeycomb support must be placed closer and closer together to prevent the reflecting surface from vibrating or sagging too much. As the density of the support locations increases, so does the mass of the supporting honeycomb structure. Thus, there is a limit to how lightweight a honeycomb core mirror can become without significantly losing stiffness and thus performance.
In addition, polishing a mirror supported by a honeycomb core back structure is problematic and may result in quilting as the polishing tool deforms the honeycomb walls and the mirror offers less resistance to the polishing tool in the areas between the honeycomb walls. As a result, more mirror material is removed at the boundaries of the mirror and the honeycomb cell walls than between the honeycomb cell walls.